The large increase in home building in recent years, the long recognized attractiveness of wood as a decorative and attractive building material and the decrease in lumber availability due to declining supply of logs and their subsequent high cost has resulted in an increased emphasis on quality production of lumber resources and the reduction of fibre waste. This is particularly so in the lumber mills where logs are cut into lumber used for various purposes.
The saws used to cut lumber, be they circular or band type, must be leveled and tensioned, i.e., "benched", so as to reduce the cut in the log caused by the saw to a minimum value. This cut is known as the "kerf" and it is most desirable to have a kerf as narrow as possible to reduce wastage. It is estimated, for example, that a saw improperly benched by only 0.001 inch can cause $12,000.00 annually in lost revenue because of the loss of wood. In addition, it is desirable to produce a quality cut. Such quality cuts can result in lumber having an appearance close to that of planed lumber which increases the price that can be obtained.
Present saw leveling operations are unsatisfactory. The basic technique is to simply use a hammer to pound the discontinuities in the saw flat. While this technique does result in relatively flat saws, hammer blows create concomitant stress associated with impact concentrations. Poor or foul hammer blows can also create permanent marks on the saw, which will result in reduced saw performance and increased saw maintenance. Furthermore, training of a "saw filer" to level a saw by hammering is a lengthy and expensive process.
Another technique utilizes saw leveling rolls. In this method, a first roll with a concave surface is located on one side of the saw and a second roll with a convex surface is located on the opposite side of the saw. This method, however, removes only discontinuities in one direction and cannot be used for tensioning or shearing.
In addition to proper leveling of the saw, it is frequently necessary to "tension" the saw. Saw tensioning creates a pair of "tire lines" on the saw which are required for proper running of the saw on the wheels of the bandmill when under sawing operation. These tire lines are created by moving a saw through tensioning rolls which have opposed convex surfaces. The surfaces are applied to the saw and act to minutely thin and thereby lengthen the saw in front of and behind the tire lines. One tire line is located immediately back of the saw teeth and is known as the "front" tire line. The other tire line is the "back" tire line and it is located on the opposite or back edge of the saw away from the cutting teeth. The front tire line is minutely thicker than the back tire line. This is so because the heat and stress created on the teeth when cutting lumber will lengthen the front tire line of the saw which will then approach the length of the back tire line and which, in turn, will allow the saw to run true on the wheels of the bandmill when the saw is in operation.